The present invention relates to an axle driving apparatus for improving the straightforward running capacity of a vehicle on a muddy road or the like, and more particularly to an axle driving apparatus which is integrally provided with a hydrostatic transmission (hereinafter referred to as the HST); axles; a power transmitting mechanism, which can easily change the speed of the HST; an oil reservoir, which can absorb an increase in the volume of oil due to an increase in the temperature of the HST; and a differential locking device, all of which are provided in a single housing.
Conventionally, an axle driving apparatus consists of a housing for an HST, axles and a power transmitting device for interconnecting the HST and axles. On the center section of the HST is disposed a hydraulic pump, provided with a vertical input shaft, and a hydraulic motor, provided with a horizontal output shaft. A plurality of pistons are disposed in the hydraulic pump cylinder block. The heads of the pistons abut against a movable swash plate. Changing the angle of the movable swash plate changes the pump capacity so as to increase or decrease the number of rotations of the hydraulic motor. The movable swash plate is slanted, thereby enabling the speed of the HST to be changed by rotatably operating trunnions supported in the housing. Each trunnion is disposed on a longitudinally slanted axis of the swash plate, as disclosed in U.S. Pat. No. 5,456,068, for example.
A speed change controller, such as a pedal or a lever, which is provided on the vehicle can be operated normally longitudinally thereof so that its motion can be transmitted to a control arm of the axle driving apparatus through a link mechanism, such as a rod, disposed longitudinally of the vehicle. Hence, it is preferable that the control arm swing longitudinally around the lateral axis. One conventional construction is provided with a vertical operating shaft, independent of the trunnions, where both trunnions and the vertical operating shaft interlock with each other. The control arm is provided at one end of the operating shaft so that the control arm swings longitudinally around the vertical axis, and the other end is constructed so that the trunnion projects at the axial end thereof from the front wall of the housing. A control arm is provided at the axial end so that the control arm swings laterally around the longitudinal axis. A complex linkage mechanism, with respect to the vertical operating shaft and trunnions, is required in the first construction described above, thereby increasing the number of parts and assembly time, making the axle driving apparatus too expensive to produce. The second construction described above requires a separate link mechanism for converting the longitudinal motion into a lateral motion, thereby requiring space to provide two link mechanisms in the vehicle, making it difficult to apply the apparatus to a vehicle of small size and increasing the number of parts required.
U.S. Pat. Nos. 5,440,951 and 5,515,747 disclose that when the HST and the mechanism for transmitting power to the axles from the HST are housed in the same housing, the housing can be filled with oil to be used as both operating oil for the HST and lubricating oil for the transmitting mechanism. In this case, a foreign object, such as iron powder, created by the rubbing of the transmitting mechanism may flow toward the HST. The iron powder or other foreign object is removed by an oil filter so as not to enter into the HST closed fluid circuit. However, the iron powder or the like may encroach on the piston and swash plate and thereby adversely affect them. The housing is integrated in part with the oil reservoir so as to enable the oil volume in the housing to be adjusted when expanded due to a rise in temperature. However, the greater the quantity of oil, the larger the increase in volume. Thus, the housing must be made larger and the reservoir therefore becomes larger so that the housing itself has to be large in size.
U.S. Pat. No. 5,094,077 discloses that in order to prevent the speed change controller equipped on the vehicle from being hastily operated by an operator, a shock absorber is provided on the control arm. The shock absorber should be disposed above the upper wall of the housing because the control arm is configured to vertically and longitudinally swing around the axis on the upper wall of the housing. Therefore, space for disposing the shock absorber without interference with an input pulley or an enlarged portion of the upper wall of the housing is required.
Further, where a differential gear is provided between the left and right axles, when one axle is idling, a driving force cannot be transmitted to the other axle. Hence, it is desired to provide a differential locking device on the axle driving apparatus for integrating the differential locking device with the HST and the axles.
The axle driving apparatus of the present invention is partitioned by an internal wall provided within the housing, into a first chamber for housing therein the HST and a second chamber for housing therein axles and a transmitting mechanism which transmits power from an output shaft of the HST to the axles. Both chambers are filled with common oil. An oil filter is disposed therebetween to allow the chambers to communicate with each other. One chamber communicates with an oil reservoir. Trunnions for the swash plate to change the output rotation of the HST are supported between the internal wall and a side plate fixed to the housing. The trunnions are disposed laterally of and in parallel to the axles. One of the trunnions projects outwardly from the housing so as to fix an arm. The shock absorber is connected thereto, thereby preventing hasty speed change. A differential locking device is attached to a differential gear differentially connecting the left and right axles. During the normal running of the vehicle, the differential rotation can be performed. When one axle is idling, both axles are adapted to be directly connected to each other.
These and other objects of the invention will become more apparent from the detailed description and examples which follow.